Key Issues Perspective: White mold in fields almost permanent

“If white mold isn’t treated, it can be devastating to soybean yields,” said Drew Spidahl, part owner of the five Ag-Tech ag retail locations in northwest Illinois. And he knows, because he has seen plenty of white mold problems in the company’s service area.

“Typically with white mold, when you find it, it is too late, and you can’t effectively remedy the situation,” Spidahl said. But white mold can be predicted in fields where it was found in previous years. “White mold shows up with high moisture and cool temperatures at the R1 flowering stage of soybeans,” he explained. Therefore, Spidahl urges his customers to plan on at least one fungicide treatment during the growing season in case those conditions occur.

The Ag-Tech locations, with the main office at Stockton, Ill., are based in an area known to have high pressures of white mold, according to Mike Weber, a Midwest Bayer CropScience (BCS) technical service representative, who helped write a training manual educating ag retail agronomists, BCS sales representatives and farmers about the fungal disease.

Sclerotinia stem rot, commonly known as white mold, is infecting fields throughout most northern Midwestern states. Northern Illinois and northwest Iowa are thought to be the most infected areas in the country for the mold attacking soybeans. White mold doesn’t just attack soybeans, it can be hosted by several crops including alfalfa, canola, clover, potatoes and sunflowers.

In fields that have had a white mold problem in the past, but not for a couple years, the fungal infection will re-occur if temperatures are in the 70- to 85-degree range and there is good moisture. The white mold develops from tiny black pellets that are in the soil from previous years when white mold wasn’t controlled. These sclerotia, or cocoons, develop in the stem of the soybean plant and drop into the soil at the end of the season; they can wait for years until the right temperature and soil moisture occurs for them to develop little mushroom-like structures at the soil surface. These mushrooms burst open and spores go up into the soybean plant where the disease establishes itself on the stem of soybean plants.

Spidahl passes along information to his soybean growers so that they are aware of things to consider. He explains how, “Some soybeans are somewhat resistant to white mold. Early planted soybeans often reach the R1 flowering stage early in the season when it can be cooler and wetter. Plus, narrow rows and heavy plant populations are contributors that encourage white mold.”

Spidahl and Weber rely on experience to know that agronomic tactics alone are only going to help minimize white mold. “You are still not going to control the disease those ways. You have to incorporate fungicide into a management program to control white mold,” Weber said.

Ag-Tech commonly recommends a preventive application of Proline fungicide near the R1 soybean growth stage. And then Ag-Tech often custom applies Stratego YLD as a second fungicide application when soybeans are at pod fill or R3 stage of growth.

“When soybeans are about 10 to 20 percent flowering, the first fungicide application needs to be made,” Weber said. “The next 14 to 20 days will determine if you need a second fungicide application to help manage white mold. If after your first application it turns dry and hot for those 14 to 20 days, the likelihood of white mold will be dramatically reduced. On the opposite side, if it is cold and wet for those days, then you will need a follow up fungicide application.”